Objective: This experiment was designed to study the change of nitric oxide (NO) content in different parts of brain in rats suffering from iodine deficiency(ID) and hypothyroidism since their fetal period. Methods: Iodine deficiency animal model was made and NO content in hippocampus(HPC), cerebellum (CE) and cortex(CO) were measured by using NO test kit. Results: Urinary iodine and serum T 3?T 4 concentrations significantly decreased and learning-memory capacity was impaired in ID rats. NO content was significantly lower in HPC and CE in ID rats than in control rats.(HPC:11.61?2.31/2.3?1 18 ?mol/g Prot;CE:10.77?5.16/4.70?1.95 ?mol/g Prot).No difference was found in cortex. Conclusion: Iodine deficiency and hypothyroidism since fetal period could affect NO level in rat brain. Different parts of brain have different sensitivity to ID and hypothyroidism.The changes of NO content in hippocampus may contribute to the learning-memory impairment in ID rats.